libidset: add embedded idset expansion support

Add two functions that simplify expansion of strings that have
embedded idsets.  For example we can represent the set of
hostnames "fluke1", "fluke2", and "fluke3" more succinctly
with an embedded idset, e.g. "fluke[1-3]".

When presented with a string containing an embedded idset,
reproducing the original set of stirngs is simplified with
the following functions:

/* Decode the first bracketed idset embedded within 's'.
 */
struct idset *idset_decode_embedded (const char *s);

/* Replace the first bracketed idset embedded in 'fmt' with 'id'.
 */
int idset_format (char *buf,
                  size_t bufsz,
                  const char *fmt,
                  unsigned int id)

src/common/libidset/Makefile.am

@@ -16,7 +16,8 @@ fluxinclude_HEADERS = idset.h
 libidset_la_SOURCES = idset.c \
 		      idset_private.h \
 		      idset_decode.c \
-		      idset_encode.c
+		      idset_encode.c \
+		      idset_format.c
 
 libidset_la_CPPFLAGS = \
 	$(AM_CPPFLAGS)

src/common/libidset/idset.h

@@ -100,6 +100,17 @@ size_t idset_count (const struct idset *idset);
  */
 bool idset_equal (const struct idset *set1, const struct idset *set2);
 
+/* Substitute a numerical 'id' for bracketed text (e.g. an embedded idset)
+ * in 'fmt', placing result in 'buf'. Returns 0 on success, -1 on failure
+ * with errno set.
+ */
+int idset_format (char *buf, size_t bufsz, const char *fmt, unsigned int id);
+
+/* Decode the first bracketed idset embedded in a string.
+ * Returns idset on success, or NULL on failure with errno set.
+ */
+struct idset *idset_decode_embedded (const char *s);
+
 #endif /* !FLUX_IDSET_H */
 
 /*

src/common/libidset/idset_format.c

@@ -0,0 +1,63 @@
+/************************************************************\
+ * Copyright 2014 Lawrence Livermore National Security, LLC
+ * (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+ *
+ * This file is part of the Flux resource manager framework.
+ * For details, see https://github.com/flux-framework.
+ *
+ * SPDX-License-Identifier: LGPL-3.0
+\************************************************************/
+
+#if HAVE_CONFIG_H
+#include "config.h"
+#endif
+#include <sys/param.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdbool.h>
+
+#include "idset.h"
+#include "idset_private.h"
+
+int idset_format (char *buf, size_t bufsz, const char *fmt, unsigned int id)
+{
+    char *p, *q;
+
+    if (!buf || !fmt) {
+        errno = EINVAL;
+        return -1;
+    }
+    if (!(p = strchr (fmt, '[')) || !(q = strchr (p + 1, ']'))) {
+        errno = EINVAL;
+        return -1;
+    }
+    if (snprintf (buf,
+                  bufsz,
+                  "%.*s%u%s",
+                  (int)(p - fmt),
+                  fmt,
+                  id,
+                  q + 1) >= bufsz) {
+        errno = EOVERFLOW;
+        return -1;
+    }
+    return 0;
+}
+
+struct idset *idset_decode_embedded (const char *s)
+{
+    char *p, *q;
+
+    if (!s || !(p = strchr (s, '[')) || !(q = strchr (p + 1, ']'))) {
+        errno = EINVAL;
+        return NULL;
+    }
+    return idset_ndecode (p, q - p + 1);
+}
+
+/*
+ * vi:tabstop=4 shiftwidth=4 expandtab
+ */